##Someone has already solved your problems

These patterns are ported from the Java examples in the O'Reilly book "Head First Design Patterns".

• Abstraction
• Encapsulation
• Polymorphism
• Inheritance

• Encapsulate what varies
• Favor composition over inheritance
• Program to interfaces, not implementations
• Strive for loosely coupled designs between objects that interact
• Classes should be open for extension but closed for modification.
• Depend on abstractions. Do not depend on concrete classes.
• Only talk to your friends.
• Don't call us, we'll call you.
• A class should have only one reason to change.